Preparation and Properties of Heterogeneous Catalysts Based on the Regulation of Reactive Oxygen Species

Author:Tian Na

Supervisor:tian xi ke


Degree Year:2019





A large number of refractory organic pollutants exist in groundwater and surface water.Advanced oxidation processes(AOPs)have emerged as the most efficient technologies to eliminate and mineralize refractory organic pollutants.Among many advancedoxidationprocesses,persulfates(peroxymonosulfate,PMS;peroxydisulfate,PS)are more stable and inexpensive than hydrogen peroxide and ozone,and produces more kinds of reactive oxygen species(ROS),which can realize the existence of reactive oxygen species with different oxidation capabilities.Therefore,this paper focuses on the development of a new heterogeneous AOP,the regulation of the types and quantities of ROS,and the improvement of the utilization efficiency of persulfate and even ROS.In this paper,the mechanism of catalytic decomposition of persulfate,the design of heterogeneous catalysts with controllable reactive oxygen species,and the utilization efficiency of reactive oxygen species are discussed.(1)A series of manganese oxide catalysts(Mn2O3)have been synthesized,and their catalytic performance in heterogeneous activation of peroxymonosulfate(PMS)for phenol degradation in water was investigated.According to electron paramagnetic resonance(EPR)and classical quenching tests,a new pathway and mechanism of PMS activation by manganese oxides,which is the formation of 1O2,have been proposed.In addition,the amount of generated 1O2 is closely related to the preparation method and morphology of manganese oxides.It was confirmed that hierarchical Mn2O3 flower microspheres have the highest catalytic activity as PMS activator,which could degrade phenol completely in 40 minutes.Because the generation of 1O2 is a self-decomposition of PMS,the activation energy of manganese-based oxides with different morphologies decreases with the improvement of catalytic performance,and the decomposition efficiency of PMS follows the same order as their catalytic performance.It is precisely because of the lowest activation energy of hierarchical Mn2O3 that PMS is more likely to self-decompose on the surface of the catalyst and produce more 1O2,which is the main reason for the improvement of the catalytic performance.(2)Cerium has been successfully doped in the hierarchical Mn2O3.It was found that 4 wt%Ce doped Mn2O3 could improve the degradation efficiency of 2,4-dichlorophenol(2,4-DCP)from 82.10%to 100%by activating PMS,and its First-order reaction rate constant could be increased from 1.86×10-2 min-1 to6.68×10-2 min-1.Besides 1O2,·OH and SO4·-were identified and involved in 2,4-DCP degradation process over Ce doped Mn2O3 according to EPR,quenching tests and XPS analysis.This is mainly due to the introduction of Ce with different valence states and the change of valence state of Mn.It can not only follow the electron transfer mechanism to produce free radicals,but also reduce its activation energy to follow the energy transfer mechanism to produce 1O2 by regulating the decomposition of peroxymonosulfate.Moreover,the contribution of·OH and SO4·-to 2,4-DCP degradation can be regulated by adjusting the Ce doping amount.We have firstly realized the regulation of ROS,which is the fundamental reason for the remarkable improvement of degradation rate and efficiency.(3)Aiming at the specific catalysis of persulfate catalyst,a catalyst which can activate both PMS and PS was proposed.A heterogeneous catalyst for the efficient activation of PMS and PS was prepared by loading Ag nanoparticles on hierarchical Mn2O3.In Ag/Mn2O3/PMS system,100%of phenol degradation can be obtained at90 min.Besides,the removal rate of phenol can reach 93.17%in PS system,and the reaction rate constant is 4.4 times higher than that of Ag nanoparticles and 11.0 times higher than that of Mn2O3.The strong interaction between Ag and Mn2O3significantly enhances the electron transfer ability of the catalyst and accelerates the formation of·OH and SO4·-in the catalytic reaction.Strong metal-support interaction not only reduces the use of Ag and improves the dispersion of Ag,but also solves the shortcomings of the specificity of conventional catalysts,which provides a new idea for the research and development of heterogeneous persulfate catalysts.(4)In addition to the regulation of ROS and the study of the mechanism of persulfate activation,how to improve the utilization efficiency of ROS and shorten the interaction distance between ROS and pollutants are the research contents of this chapter.A heterogeneous catalyst supported on active carbon(AC)and Ag-AgI heterostructure was designed and synthesized.2%Ag-AgI/AC can completely degrade 2,4-DCP within 90 min under the conditions of 0.05 g/L catalyst dosage,5mM PS dosage and 100 mg/L 2,4-DCP.With the strong adsorptive and catalytic abilities of AC,the mixed valence Ag(Ag0 and Ag+)and Plasma properties of Ag,different kinds of ROS(1O2,·OH and SO4·-)can still be regulated.During the activation of PS by Ag-AgI/AC catalyst,ROS is mainly 1O2 and·OH,and only with a small amount of SO4·-.In addition,due to the enrichment effect of AC on pollutants,the interfacial catalysis of PS to produce ROS and the simultaneous enrichment and degradation of pollutants at the interface have been realized.